The functions of a membrane protein include cell cohesion, relaying signals between the inside and outside of a cell and transporting proteins across the membrane. A membrane protein is a protein that is attached to a cell and interacts with biological membranes. Each type of membrane protein has a different function.
Each membrane protein can be classified into either integral membrane proteins, which interact with the membrane phospholipids, or peripheral membrane proteins, which temporarily stick to the membrane and help with electron transport.
Some membrane proteins help cells identify one another. This is especially true with the cells of the immune system. Immune system cells have to recognize one another to prevent attacking each other.